As mobile telephones have spread rapidly in recent years, an increasing number of people have their own personal mobile telephones and are thereby able to communicate with one another with much ease.
However, in order for a calling party to contact someone in his/her family, or someone in a store or an office without specifying a particular someone, the calling party needs to know all the telephone numbers of the mobile telephones owned by the members of the family, the store, or the office. In this case, the calling party also needs to repeat an operation for connection on the mobile telephone until he/she can reach someone in the family, the store, or the office. The calling party may find it inconvenient to repeat such an operation.
Given the above factor, the following technology has been used: all the telephone numbers of a plurality of mobile telephones are pre-registered as belonging to one group on a telephone exchange that is placed on a premise. If the telephone exchange receives an incoming call in which a representative telephone number representing the pre-registered group is dialed, it will call every single telephone number that belongs to the group all at once, and connect the calling party to any mobile telephone that has answered to the incoming call.